By Richard Woods From-South African Yachting, May 1990

THE phrase 'home-built catamaran' conjures up an image of part-completed, slab-sided hulls festooned in polythene and plastic sheeting, plumbed into the main drainage system and providing a weekend hobby on a long term basis for land-based dreamers who no more want to go near the water than they want to fly.

This is unfortunate because the true picture is of seaworthy boats sailing the seven seas, safe, secure and substantial. These boats make no headlines because they are built without fuss and often sail off to far horizons and are undistinguishable from production boats. The key to successful homebuilding lies in the choice of designer and his plans.

There is no hope of producing a professional-looking boat if the design and plans are amateurish. Surprisingly, success is also unlikely if you work from plans of a production boat modified for home-building. The only sensible approach is to buy plans that were specifically drawn for home-building by a reputable designer. We have built 10 catamarans for our own use in the last 10 years, ranging in size from 14 to 35 feet and using tortured ply, foam sandwich and cold-moulded construction methods among others.

Yet we are by no means professional builders. Currently we are building a 30-foot strip-planked catamaran in a temporary shed in our backyard. A job we hope will be easier now that we have a decent jigsaw and power plane. Partly due to our own lack of facilities we always try to design boats that anyone can build. As far as we are concerned this means designing boats that use flat panels as much as possible.

The photo shows that this does not mean having a boat that looks like a box. Admittedly this boat (our 35 foot Banshee) has round bilge hulls below the waterline (where you cannot see them). What you can see, however, is a boat made of flat panels. The term flat panel is mis-leading because it really refers to single curvature panels. These single curves allow a huge variety of shapes to be built in almost any material.

THE LOGIC FOR BUILDING IN FLAT PANELS

Although round bilge hulls have the least wetted surface area for a given displacement and so are considered the optimum shape, a close approximation to a round bilge hull can be achieved with a single or double chine hull. On the smaller boats a dory hull shape works well, simply because the amount of boat in the water is so small. Any aspiring home-builder is most concerned about building the hull. This is understandable since it is usually the first job to tackle.

However, anybody who has built a boat will say that building the hull is the easy part, it is the fitting out that is difficult and takes the most time. As an indication the two hulls of a production Banshee can be built in under 100 hours, yet it takes 2500 hours to finish the boat. In fact it takes longer to install the electronics than to build the hulls!

These figures also show how big a commitment boatbuilding is. The average person works 2000 hours a year at his job, so 2500 hours is the equivalent of 15 months full time work. It is a major commitment not only for the builder but also for his family. The first catamaran I built (a 30-footer) took less than six months to build single-handed, while working 40 hours a week at my job as designer. The motivation came from the fact that until the boat was finished I had nowhere to live, let alone a boat to sail.

Building in a yard where others were doing the same also helped - problems shared are problems halved. Since a boat takes such a long time to build, any techniques that can speed up the building should be seriously considered. Speed in building should really be given a higher priority than say ultimate sailing speed or comfort. Many monohull builders learned about single curvature panels when they built multi-chine steel hulls. Steel is unsuitable for multihulls under about 100 foot (aluminium under about 60 foot), so multi hull builders' materials are wood and fibreglass. Plywood is usually considered the automatic choice for home-builders. Fortunately with the advent of epoxy glues many of its drawbacks have been overcome (although epoxy has some of its own, mainly because it is highly toxic.)

However, more builders should consider building fibreglass hulls. The two normal reactions to this comment are "you mean foam sandwich," or "you need a mould." In fact, there is a simple way of producing a hull with a conventional gelcoat finish without using foam or a complicated mould. The main disadvantage of foam sandwich, apart from its cost, is that the outside surface is rough. It needs a lot of filling and sanding to get a smooth hull. Note I said smooth, not fair, because it also requires a lot of care to get a fair hull since it is difficult to judge the fairness when fitting the foam sheets. Changing a shape from a double curve to single curve helps fairing up considerably.

Compound curves are supposed to add extra stiffness, but multihull topsides are always fairly flat, so the extra curvature adds little. The main attractions of foam sandwich are its light weight and high strength, but this comment has to be qualified. There has to be a certain thickness of glass on the outer side of the foam to protect the core from impact damage. Top monohull race boats now have skins so thin that only the paint keeps them watertight and they cannot be lifted by slings round the hull without being crushed. On multihulls under about 35 foot the use of a foam panel as opposed to one of solid glassfibre usually results in only a minor weight saving. The saving is irrelevant on a cruising boat.

Even we are surprised at the room inside a modern, wide beam multihull. A boat over 35 feet for family cruising is probably too large. We would not recommend a boat over this length for an amateur builder. Thus most home-builders should be able to use the solid glass flat panel technique. It may sound difficult and unfamiliar but making the panels is extremely simple. The photographs of a 27 foot catamaran under construction show the basic stages involved, while the table shows the time required to build the boat to a sailaway state.

MOULD

The "mould" is a flat worktop made of glossy melamine- or formica-covered chipboard (the material used for shelves and kitchen worktops). Resin does not stick to these surfaces so gelcoat can be applied directly. It is not necessary to make the whole hull side in one go. Making them, for instance, in eight-foot sections means it is easier to heat the workshop and less space is required until they are finally joined together before final assembly.

After laminating the hull panels stringers are fitted and then they are cut to the exact sizes given on the plans, offered up to the bulkheads and glassed along the keel (and chine if necessary) and to the bulkheads. This procedure only takes a few hours. Although the joints will need filling and sanding the topsides have a perfect gelcoat finish, often better than that of a production boat.

POTENTIAL

As you get more used to the concept of melamine flat panel moulds the potential uses begin to grow. Simple moulds can be made for galley worktops, steps, shower compartments or lockers. Both male and female moulds can be knocked up quickly. All joints need rounding to allow the moulding to release easily; inside joints can be made with plasticine, outside joints of timber battens rounded off. Only the timber needs coating with a release agent before laminating. I have suggested using simple melamine moulds to help fit out the interior because often it is not the external appearance that gives a home-built boat away but the internal finish. Flat panel topsides help fit out the interior more quickly, since making something fit to a straight line is easier than having to scribe to a curve. Besides being more practical a moulded gelcoat interior makes the boat look professionally finished.

DECKS

Most decks have single curvature and need to be foam sandwich for stiffness. This is particularly true on bridgedeck cabined catamarans because, although a flexible deck is usually strong enough, it is disconcerting to walk on. It is seldom worth making moulds for decks. Normally we cut the foam to size, glass the inner skin and offer it up to the boat, bend it to the required camber and then glass the outer skin in situ. This results in the usual rough finish, but a layer of surface tissue and a quick skim of filler should be enough since non-slip deck paint is used over most of it, hiding small lumps and hollows.

SATISFYING

Building a boat yourself in your spare time is a satisfying and for some even a pleasurable experience. However, for most people it is the end product - the boat and the sailing that are important, not the building. You will learn many new skills and, more important, will know how to maintain and repair the boat when required. Many beginners have completed large projects successfully. Often organisational skills are more important than boatbuilding experience.

One final comment. It may well take years to build your dream boat. However, once completed she is often a dream for only three years: year one is spent getting used to it, year two enjoying it, and year three is spent realising what could be different. Then one starts looking for another design. So when building your boat bear in mind that you will probably sell it again and resale value is important. So remember that spending 10 percent more money and 10 percent more time and effort while building can increase the resale value by 50 to 100 percent.